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[讨论] sd初始化时连发74个时钟有何用处?

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发表于 2006-9-29 09:22:00 | 显示全部楼层 |阅读模式
sd初始化时连发74个时钟,是不是纯粹为了给予sd卡的上电时间.请牛人指教.
 楼主| 发表于 2006-9-29 13:51:00 | 显示全部楼层
我考虑host在检测到插入信号后,将CMD线拉高,然后发送74个时钟,可能是为了让卡端有充足的初始化时间,然后还预备接接收SPI、sdio、sd mmc选择信号
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发表于 2007-6-20 14:52:00 | 显示全部楼层
SD卡规范上是这么写的:
After power up, the host starts the clock and sends the initializing sequence on the CMD line. This sequence is a contiguous stream of logical ‘1’s. The sequence length is the maximum of 1msec, 74 clocks or the supply-ramp-uptime[/COLOR]; the additional 10 clocks (over the 64 clocks after what the card should be ready for communication) is provided to eliminate power-up synchronization problems.[/COLOR]

从描述中可看出,主要解决上电后总线通信的同步问题吧。
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